All eukaryotes have a circadian system responsible for organizing many functions on a daily basis. At the heart of this system is a circadian oscillator that has to be regulated or entrained in order for the oscillator to be adaptive for the organism. Our long term goals are to understand the biochemical events involved in entrainment and to identify molecules involved in the oscillating mechanism itself. The isolated eye of Aplysia produces a circadian rhythm and this rhythm is regulated by light and the neurotransmitter serotonin. The proposed research will define biochemical events in the serotonin and light entrainment pathways and it will identify putative molecular components of the circadian oscillator. First, we will identify specific proteins whose synthesis and state of phosphorylation are regulated by serotonin or light. Then these proteins will be subjected to a number of tests to examine if the proteins are involved in entrainment by serotonin or light. Some of the criteria for a component of the circadian oscillator are the same criteria for an element of the entrainment pathway. Thus, the molecules that are associated with entrainment will be subjected to further tests to examine if they are components of the circadian oscillator. In particular, we will examine cyclic nucleotides, a 34K protein, and other proteins that emerge from the synthesis and phosphorylation work of this proposal. After proteins are identified as putative components of the oscillator, we will make monoclonal antibodies to the proteins. These antibodies will be used as probes to localize the proteins using immunohistochemistry. The research of this proposal should lead to an understanding of the cellular and biochemical regulation of a circadian oscillator. Our results should also pave the way for a molecular analysis of circadian timing. An understanding of the mechanisms that regulate circadian oscillators should hlep elucidate disorders associated with circadian rhythm abnormalities. Evidence indicates that circadian rhythms may play a role in the maintenance of mental health: in sleep disorders, in manic-depressive illnesses, and in the ability to learn and function normally. Our research, whose purpose is to identify molecular elements of circadian timing systems, should help elucidate the role of circadian rhythms in mental health by focusing attention on specific types of molecules that may be related to causes of mental illness.